Where thumb/thumb.php is the relative path to your timthumb script (which may be named differently for you) and which is preceded by bloginfo('template_directory'); which will give you the path to your theme + /thumb/thumb.php

Now the only other part you need to mess with is essentially the h=XXX and w=XXX where XXX is equal to your size in pixels that you'd like your thumbnails.

This will set you in the right direction.

Although I haven't tested that many slideshow plugins I'd say there ought to be one out there that handles variable image sizes for thumbnails.

A plugin that I like for its simplicity is Meteor Slides which is based on the jQuery Cycle plugin - so you can extend it to have thumbnails if you want or you can just as easily go the manual route.

Bit of a late response but thanks for your answer userabuser. This is exactly what I'm looking for but I can't get it to work with the code you supplied. I have an example here but it's not working ttmt.org.uk/wordpress - Any help?
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user668499Apr 26 '12 at 11:12